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Using theoretical results from complex rotation calculations and data from experimental photoionization cross sections, the quantum defects, the widths, the oscillator strengths and the shape parameter of Rydberg series of autoionizing 1 P o resonances in helium, excited with synchrotron radiation from the ground state, are reviewed and analysed systematically. The relation of these resonance properties to the propensity rules for radiative and non-radiative transitions in two-electron atoms is established.

The double-excitation 'I" Rydberg series of He, converging to the N=4 to 9 thresholds, were studied by high-resolution photoionization using synchrotron radiation. Both the principal series with correlation quantum numbers K=N -2 and the secondary series with K=N -4 could be resolved up to previously unobtained n values. This allows a substantially improved analysis of the series with respect to energies and linewidths, leading to an improved understanding of the interseries interferences. The data are in excellent agreement with calculations based on the complex-rotation method.PACS number(s): 32.70.Fw, 32.80.t, 31.50.+w, 31.25.Jf

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An experimental and theoretical study of ground-state photoionization of neon is presented in the photon energy range between 44 and 53 eV. This portion of the spectrum is characterized by a singly excited Rydberg series 2s2p 6 np, and by overlapping doubly excited Rydberg series 2s 2 2p 4 3snp and 2s 2 2p 4 3pnl (lϭs,d).With the use of synchrotron radiation of Х3 meV spectral resolution, numerous hitherto unobserved resonances were resolved, including some which exhibit relativistic effects. To identify resonances observed here and in earlier works, we employed numerical calculations, which combine the eigenchannel R-matrix method, multichannel quantum defect theory, and the recoupling frame transformation. These nearly ab initio methods account for most of the observed features in the spectrum, including a class of spin-induced relativistic effects.